Crazy Material That You Can Make at Home That Actually Bends Light!

hey everyone today I'm going to be showing you a crazy cool experiment that you can probably do at home that shows you how to bend light but before I do that experiment I want to first convince you that light moves in a straight line okay proof number one the light usually moves in a straight line you can't see me right now so if light didn't move in a straight line you'd be able to see me right now because the light would just come from my face go around this block here and go to the camera but you don't see me right now and the reason is because this is in the straight path between me and the camera but as soon as I move it out of the way then you can see me because the light can go straight from my face to the camera but you may say if light only moves in a straight line how come someone that's in front of me can see my face and someone to the side of me can see my face if he only goes in a straight line wouldn't it just hit the person in front of me well no because even though light always moves in a straight line it doesn't say which direction that straight line is facing so the straight line could be this way or that way it turns out that the light hitting my face has light going all different directions so there's a bunch of light pointing this way this way this way this way this way and this way and so people all around me can see my face and again you may say if light moves in a straight line how come a laser looks like this but a flashlight looks like this see how the laser just goes in one straight direction but a flashlight curves like this does this mean that flashlight light curves and doesn't go in a straight line but laser light goes in a straight line well no it doesn't mean that at all both of these lights are going in a straight line it just means that a flashlight has light that's going this direction this direction this direction this direction this direction this direction and this direction whereas a laser light only has light that's going this direction so you can see that all of these rays of light are moving in a straight line but they're just pointing different directions so all light moves in a straight line but it doesn't always point the same direction so what I want to show you today is not just light that's pointing in a different direction but light that goes like this so now that you believe me that light does go in a straight line always the question is why does it go in a straight line why is light always moving straight why doesn't it ever look like this well there's a lot of answers to this question and it can get really complicated depending on how you look at it but today I want to give the easiest right answer remember I showed you in a previous video that light has momentum and I showed you this by reflecting light hanging off a reflector in a vacuum and I showed you that you could turn the reflector just by shining light on it now there's a specific law in physics called conservation of momentum and it means that momentum is always conserved so if you have momentum in one direction it has to continue in that direction so just like this ball has momentum it means that once I start rolling this ball in a specific direction it's going to keep going that direction and the only way it can change directions is if I add momentum to the system so as a result of that light always moves in a straight line for the same reason that any object that we throw moves in a straight line from when we throw it now the conservation of momentum explanation for light moving in a straight line is the easiest one that's also correct but there's also a bunch of different explanations you could use a lot of them having to do with quantum mechanics the quantum mechanical explanation has to do with superposition mainly that the wavefunction of all of the photons being emitted cancel each other out in every direction except the forward direction straight ahead of it so at this point we know why light moves in a straight line and we know that it does always move in a straight line so the speed of light in a vacuum is a constant that never changes and it's the fastest that light can go but when you put light in different materials then you start to slow down that light a little bit so let's say I put it in this material that's kind of dance so these are atoms that are absorbing than remitting the light so it's a transparent material the light goes straight through it but what happens if the light hits an atom gets absorbed and then re-emitted and so it kind of takes some time to get through so the time in between atoms it's actually moving at the speed of light in a vacuum but this time of absorbing and then remitting by these atoms adds to the overall time so it appears as though light is moving slower in a material that has more atoms and so if you had a material that was really dance then it would appear that light moves really slow through it now this ability to effectively slow down light in a material is called the materials refractive index so this has a high refractive index this has a medium one this has a low one now the effect of light moving slower ends it goes through a denser medium is actually really interesting because what it causes it to do is that as soon as the light enters that new medium it causes the light to bend so for example using my acrylic vacuum chamber lid and this laser here you can see how the path of light bends as soon as it enters the acrylic here if the acrylic straight on it goes straight but once I change the angle it gets a it gets really dramatic so you can see how dramatic the bend is here as it comes in at this angle and hits the acrylic now the light is going this direction so it changed the direction of light instead of going this way it changed it to go this way now the reason that light curves when it hits a material is because light always takes the path of least time between two points for example it would take light actually longer time if it went in a straight line when it entered a denser material because it can move faster in this material than this material so it will travel longer in the material that can it can move in faster and it will travel the shortest distance in the material that it moves slower in to get to Q the fastest and because the refractive index is actually dependent on the wavelength of light that means that you can actually spread out and separate the different colors of light just by passing it through two different materials so in this case we're going from air into glass so I have a white light source here and it hits this and spreads out the light and then you can see on the wall here all the different colors that are actually in that white light so this is because the red light moves at a slightly different speed in the glass then the violet here and so that means that they're bent a little bit different and because they're bent a little bit different they come off at different angles so they can get split up like this so now at this point now we know that light always moves in a straight line but if it hits a different material with a different density then it changes directions but at that point once it's in that new material it still moves in a straight line so no matter how hard we try with those other materials light still ends up going straight in whatever material it's in but now I want to show you a special material that within that material light doesn't even go in a straight line so even though it's staying within the same material you'll see the light actually form kind of an arch it'll curve within the material itself let me show you what I mean okay so I've filled my vacuum chamber up with a very specific material and what this material is going to do is towards the bottom when I move my beam of laser down towards the bottom it's going to bend it so that it points at the bottom instead of just going straight okay here we go shining my laser through it look what happens as it gets near the bottom look how it looks like it's attracted to the bottom it's a curves [Music] [Music] example if I drop this ball in here so you can see how the light can come above the ball but then hit below it it's pretty cool so what I've created here is called a gradient index material and what that means is that the material that's in here is not one consistent density but it's higher density at the bottom and lower density at the top and so what that means is that as light gets towards the bottom it's going to bend more so what's interesting about this is watch what it looks like as we move low it looks like the bottom of the chamber is bowing up so you can see the ball just sitting there like normal from above and then I'm gonna come down and see what it looks like as I move as I move lower here let's see when we can stop seeing it now so we can see it still we can see it and see it now I'm below the box but I can still see the ball okay so there's the ball now as I move down I'm gonna get below the edge of the box but I can still see the ball so I'm a few inches below it and I can still see the ball right there it's pretty cool in fact a little bit lip better than laser light you can follow the path of the bottom corner of the box and look how bent it looks the watch does I get down low watch the background here watch how it lenses everything in fact it makes it look like there's a slope here so you can see the edge going up there but there's actually not a slope there it's actually just flat and see it's just flat like that so you can actually create something like this yourself just by using water and sugar so that's all I did here is fill this up with water and then put a layer of sugar on the bottom and I let the layer of sugar sit there for about 24 or 48 hours so the sugar dissolved but it didn't dissolve evenly throughout the whole container it just stayed on the bottom because the sugar water is more dense than regular water so all the sugar that dissolved in the water stayed at the bottom basically what that does is create a density gradient where it's densest at the bottom and least dense at the top so if you think that you haven't seen this phenomenon caused by this gradient index you're probably wrong because this is the same phenomenon that causes mirages on roads so a mirage happens on a hot road because the light from the sky is coming down at an angle but the air right above the road is a little bit hotter than the air in the sky and so that causes that air to be a little bit less dense and so it bends it the opposite way than what we saw in my experiment here it bends it up more so basically the light comes down and it hits that less dense material and it gets bent up a little and then it can shine kind of straight into your eyes as you're driving so basically you looking at it it looks like the sky is actually in the road because you're seeing light that you assume is straight but it's actually being bent from the sky and hitting you in the eye hey everyone thanks for watching another episode if you enjoyed this video and you haven't subscribed yet remember to hit the subscribe button and hit the bell to be notified when my latest videos out and if you haven't checked it out yet head over to the action lab comm did check out the action lab subscription box and thanks for watching and I'll see you next time

Channel: The Action Lab

Views: 1,792,288

Keywords: light, bend light, light bender, cool science, science experiment, how to make, science experiments to do at home, home science, diy activities, diy, the action lab, action lab, action, top 10, science project, for kids, vacuum chamber, venus fly trap, stretch armstrong, iron man, foil ball, vac man, how to, blackest black, black 2.0, zombie ant, brightest flashlight, black 3.0, self pouring, 32000 lumen, is water wet, science tricks, blackest material, life hacks

Id: 968gVUAY9Mg

Length: 13min 1sec (781 seconds)

Published: Thu Feb 14 2019

Reddit Comments

[u/Saifeldin17]

This video is very informative about light. He talks a lot about how light works, how it refracts, why it refracts, etc. At about the 7:55 mark he demonstrated an experiment where he created a refractive gradient using water and sugar. You can see that the ball he filmed looked very distorted and would not disappear even when he lowered the camera several inches below the counter. I think it showed how a flat plane and a big gradient index sufficient enough to make the ground look curved would not work properly in reality for two reasons:

1. the objects would look very heavily distorted

2. the objects do not disappear below the horizon

Please let me know if there's anything I've missed. The channel is The Action Lab and makes really good content. This video does not talk about flat earth but I found his information extremely useful.